Challenges and prospects in the catalysis of electroreduction of nitrogen to ammonia

Abstract

Ammonia is a widely produced chemical that is the basis of most fertilisers. However, it is currently derived from fossil fuels and there is an urgent need to develop sustainable approaches to its production. Ammonia is also being considered as a renewable energy carrier, allowing efficient storage and transportation of renewables. For these reasons, the electrochemical nitrogen reduction reaction (NRR) is currently being intensely investigated as the basis for future mass production of ammonia from renewables. This Perspective critiques current steps and miss-steps towards this important goal in terms of experimental methodology and catalyst selection, proposing a protocol for rigorous experimentation. We discuss the issue of catalyst selectivity and the approaches to promoting the NRR over H 2 production. Finally, we translate these mechanistic discussions, and the key metrics being pursued in the field, into the bigger picture of ammonia production by other sustainable processes, discussing benchmarks by which NRR progress can be assessed.

Recent Advanced Materials for Electrochemical and Photoelectrochemical Synthesis of Ammonia from Dinitrogen: One Step Closer to a Sustainable Energy Future

“…Treating the 15 N 2 gas with sulfuric acid overnight before the experiment has been reported in literature to remove impurities . The protocols summarized by Suryanto et al and Anderson et al are recommended here for proof of NRR . Another pitfall is the stability issues associated with the catalysts.…”

“…As a small polar molecule with a very high aqueous solubility, NH 3 not only dissolves in aqueous solutions but also adsorbs onto surfaces of experimental devices such as tubes and reactor chambers in a traceable amount especially for labs conducting NH 3 related experiments . While the current electrochemical and photoelectrochemical methods typically demonstrate low NH 3 yields in the range of 10–1000 nmol, these adventitious NH 3 molecules could compromise the accuracy and validity of measured NH 3 yields, possibly generating misleading results. Therefore, it is vital to apply effective and accurate NH 3 detection methods in combination with the prepurification of reaction systems to trace the N‐source, eliminate the contaminated NH 3 molecules, and validate the results of NRR.…”

“…As a result, ion chromatography and isotopic tracer with labeled 15 N should be conducted to rule out the misinterpretation of catalytic activity caused by external interference and confirm the origin of detected NH 3 . In this regard, Anderson et al and Suryanto et al highly recommend a standard NRR protocol involving the quantitative isotope measurements …”

Antiperovskites with Exceptional Functionalities

“…In summary, the investigation of antiperovskites for electrochemical applications may open a new field in developing novel materials for energy generation and storage. Taking advantage of numerous controllable nanosynthesis methodologies and material design principles, one may extend the application of antiperovskite‐based nanomaterials to Li‐batteries, CO 2 or N 2 electroreduction, and more catalytic systems that arouse general interest. Substituting precious‐metal catalysts with low‐cost antiperovskites is expected to be a new direction.…”

Atomic Modulation, Structural Design, and Systematic Optimization for Efficient Electrochemical Nitrogen Reduction

“…Therefore, nitrides can be said to exhibit NRR performance only when the NH 3 production rate is larger than or equal to their decomposition rate. Additionally, some control experiments can also be undertaken to determine the origin of NH 3 , according to the procedure proposed recently . During NRR, both the anion in the metal compounds and the cation (Mn) can escape, leading to a defective, oxygen‐abundant surface structure of Mn 3 O 4 for more favorable NRR …”